American Dictionary of the English Language

IR'RITABLE, adjective [from irritate.] Susceptible of excitement, or of heat and action, as animal bodies.

1. Very susceptible of anger or passion; easily inflamed or exasperated; as an irritable temper.

2. In physiology, susceptible of contraction, in consequence of the appulse of an external body.

In general, there is nothing irritable in the animal body, but the muscular fibers.